Abrasive articles generically known as structured abrasive articles are sold commercially for use in surface finishing. Structured abrasive articles have a topographically structured abrasive layer affixed to a backing. The structured abrasive layer has a plurality of shaped abrasive composites with each composite having abrasive particles dispersed in a cross-linked binder. In many cases, the shaped abrasive composites are precisely-shaped using a mold to form various geometric shapes (e.g., pyramids). Examples of such structured abrasive articles include those marketed under the trade designation “TRIZACT” by 3M Company, St. Paul, Minn. Structured abrasive articles can be used in the automotive industry to remove defects in automotive clear coats based on urethane, acrylate, or silicate chemistries. An abrasive article particularly suited to removing clear coat defects is available under the trade designation 466LA-3M TRIZACT FINESSE-IT FILM.
Structured abrasive articles can lack aggressive cut upon initial use, with improvements in cut seen with continued use. This can occur because the abrasive particles are buried in the cross-linked binder within the body of the abrasive composite and are not available for abrading. One technique used in the art for addressing the problem of lower initial cut has been to precondition the outer surface of the structured abrasive article, prior to its initial use, using another abrasive article or an abrasive slurry to abrade the outer surface. However, such a technique lacks precise control and is time consuming for large scale production of abrasive articles.
Another technique involves applying loose abrasive grains on top of an abrasive slurry before embossing a pattern to form the structured abrasive layer and then curing the abrasive slurry as disclosed in U.S. Pat. No. 5,863,306 to Wei. However, many of the abrasive grains on the outer surface are still covered by the cross-linked binder in the abrasive slurry as it is squished through the abrasive grains and rearranged by the embossing process. Furthermore, many abrasive grains are left unbonded or weakly bonded to the outer surface of the abrasive layer. This can cause problems when making the abrasive article and cause undesirable performance when using the abrasive article. To combat these issues, a subsequent application of an additional top size coat as discussed in U.S. Pat. No. 6,451,076 to Nevoret is typically required, which increases costs and can reduce initial cut rate since the abrasive grain is no longer fully exposed.
Another technique involves using a water-soluble polymer to position abrasive grains on the structured abrasive layer as discussed in U.S. pending patent application Ser. No. 11/777,701 filed on Jul. 13, 2007 entitled “Structured Abrasive Layer, And Method of Making and Using Same.” However, water is needed during use of the abrasive article to dissolve the water-soluble polymer, and it takes time before the loose abrasive grains can erode the surface of the structured abrasive layer exposing the abrasive particles held within the shaped abrasive composites.
Another technique involves using a low energy plasma etching process as discussed in JP2001334473A, which is applied to a polishing article comprising a single layer of abrasive particles having a uniform height. However, the technique disclosed results in anisotropic etching which would not uniformly etch a structured abrasive article having significant topography for the shaped abrasive composites that form the structured abrasive layer. The disclosed technique uses lower pressures, power settings, and either pure oxygen or argon gases, which results in anisotropic etching conditions. These conditions only etch the planar surfaces of the abrasive article parallel to the backing. If the disclosed etching conditions were used to plasma etch a structured abrasive article, areas of the structured abrasive layer that are not parallel to the backing, such as sloping or vertical sidewalls of the shaped abrasive composites, would be etched less or not etched at all. The resulting abrasive article would have significant non-uniformity occurring as a result of the anisotropic etching process.